The invention relates to a procedure for controlling a thermal installation which includes at least one thermal regenerator through which a process liquid circulates for the purpose of maintaining an adjustable supply temperature of the process liquid. At least one heat exchanger is provided through which the process liquid flows, connected with the regenerator via a supply pipe and a return pipe, and one circulation pump is provided which is located in one of the two pipes and whose driving motor is part of an electric circuit; furthermore, the invention concerns an arrangement for carrying out this procedure.
Today it is usually customary for the control of a central heating installation to design the oil firing of the boiler with its own boiler thermostat for maintaining a constant feed temperature to the radiators as a system in itself, whereby the process liquid is kept in circulation primarily by a circulation pump.
A room thermostat adjustable to a set temperature in one particular reference room, usually a living room, is selected. The room thermostat controls a butterfly valve or a three-way valve for a residential unit in order to allow the required process liquid to flow through the radiators as soon as the room temperature falls below the set temperatures.
The valves and, depending upon the type of control, the pump are shut off again when the desired temperature is reached or slightly exceeded. These switching procedures can also be activated by other sensors, for example, by an outside thermostat located outdoors that is adjustable to any limiting value desired.
The disadvantage of this and similar controls is that they do not take into account the return temperature of the process fluid which may be high or low. When such a control system is used in an apartment building without having an additional heat counter, it is impossible to divide fairly the heating costs used by the individual tenants.
Disregarding the all inclusive billing of heating cost according to living area which is still customary and which completely ignores the actual consumption of the individual, then the measurement of the flow of heating water pumped through a particular floor or in an apartment is still the best solution at the present time. The disadvantage is, however, that the volume of heating water that has flowed through is measured, not the actual amount of heat consumed, taking into account the temperature in the supply and return pipes.
An improvement in this regard is well know from a central heating installation with a self-regulating flow valve, which by taking into account the temperatures, maintains constant the amount of heating water flowing through. The temperature in the supply and return pipes is measured in a resistance thermometer constructed as a temperature/voltage converter and transmitted to an operational amplifier in which an output signal is formed corresponding to the temperature difference. This is transmitted to a voltage/frequency converter, which generates impulses of different frequencies the number of which is accumulated. This arrangement only has one temperature-dependent measuring device for the amount of liquid carrier through and offers no control possibilities for the operation of the installation. A further disadvantage is the complicated electrical instrumentation that is necessary.
For refrigeration plants, for example, air conditioning in the chemical industry or for the operation of cold storage units, similar situations and requirements exist as with heating installations and thus basically the same demands are placed on an efficient control device.